Israel Water Context

9. The Mountain Aquifer

The mountain aquifer is the largest of the subsurface water reservoirs in Israel. It extends from the Beer Sheva-Dimona-Dead Sea area in the south to the Binyamina-Bet Shean area in the north and its contribution to the water economy is estimated at ~600 million m³/yr, that is, around 30% the total consumption. The aquifer is fed from rains falling on the limestone and dolomite exposures of the Judea Group (of Albian-Turonian age) and on the mountain ridge, and flows to the natural drainage areas. The mountain aquifer is divided into three main basins, in accord with the direction of flow in them: in the western and southern part, the Yarqon-Taninim basin; in the northern part, the Shekhem (Nablus)-Gilboa basin; and in the eastern part, several small basins – the eastern basins.

   The water potential in the Yarqon-Taninim basin is, on average, ~360 million m³/yr, and today is fully exploited in hundreds of boreholes. Most of the boreholes are located at the foot of the central mountain ridge. To the east the thickness of the active aquifer thins and conductivity is low, and further west boreholes must be drilled to great depth in order to penetrate the layers covering the aquifer. The natural outlets of the Yarqon-Taninim basin were two large springs – the Yarqon springs in the Tel Aviv area, ~220 million m³/yr, and the Taninim springs in the Qesarya (Caesaria) area, ~100 million m³/yr, in addition to the small seepage to the Mediterranean Sea. Today the basin is exploited intensively, and as a result, the flow from the Yarqon springs almost completely diminished and the discharge from the Taninim springs decreased by around 70%. In order to prevent various salinization phenomena resulting from the intensive pumping, the Water Commission set minimal levels which must not be exceeded, and the aquifer is monitored in around 200 boreholes. Because of its size, the basin also serves as a reservoir for absorbing surplus water from other reservoirs, and as of 1970 ~16 million m³/yr, on average, has been penetrated into it (wherein the last ten years the average amounts dropped below 2 million m³/yr).

   The drainage in the Shekhem (Nablus)-Gilboa basin is from the city of Shekhem (Nablus) northward to Jenin and Bet Shean. In addition to rains falling on the Judea Group, the aquifer is also fed by rains falling on the Avedat Group (of Eocene age). The water potential in the basin is ~140 million m³/yr, whereby its discharge today at its natural outlets in springs flowing at the foot of the Gilboa Mountain, in the Bet Shean Valley and in the north of the Rift is ~70 million m³/yr. In addition to this a total of ~76 million m³/yr is exploited in the basin in tens of shallow boreholes concentrated in population centers in the mountain area and also in the area around their outlets.

   The area extends from the east to the ridge of the mountains, from Bardala in the north, through Ramallah, Jerusalem and Hebron to the Arad Valley in the south, drains to several small basins in the Jordan Valley and to the Dead Sea. In its northern part, its natural outlets are small springs in wadis that lead to the rift: Wadi el-Malih, Nahal Tirza (Fari'a), Peza'el (Fasayil) and Perat (Qelet) (in the Jericho area), and a little surplus flow to the Jordan River channel. In its southern part, its natural outlets are large springs at the Dead Sea shore: Zuqim (65 million m³/yr), Qane and Samar (35 million m³/yr) and En Gedi (~3 million m³/yr), and also non-monitored sub-marine flows, adjacent to the Dead Sea itself. The small basins in the Jordan Valley are exploited in boreholes in two main areas: the mountain ridge area (in some of the places, such as in the Herodian area, most intensively), and in the Jericho area, where pumping ranges between ~31 and ~42 million m³/yr.

   The quality of the water in the mountain aquifer is very good. The salinity of the water in the area of the exposures is 30-50 mg/Cl/l and increases with distances from the areas of the exposures to about 200-300 mg/Cl/l. In sharp contact beneath the freshwater body in the Yarqon-Taninim basin, there is a saline water body. Intensive exploitation of the Yarqon-Taninim basin will lead, among others, to an increase in the salinity of the water in the layers currently saturated with fresh water. In the north of the basin, the phenomenon was observed as a result of overpumping in the well located at the foot of the mountain ridge. In the northern Negev, pumping is done parallelly from two water bodies (the fresh and the saline) in order to prevent the spread of the saline water northward.